Unique Spermatozeugmata in Testes of Halfbeaks of the Genus Zenarchopterus (Teleostei: Hemiramphidae)

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Abstract
Testis structure in the atherinomorph genus Zenarchopterus has been examined in 11 of the 18 known species. While testis type is typical of that described in the Atherinomorpha, the genus is unique because: 1) in all species examined, sperm coalesce within the efferent and main testis ducts to form extremely elongate spermatozeugmata; and 2) the testis is divided into spermatogenic anterior and aspermatogenic posterior parts. In the posterior part of the testis, in some species, secretions by the columnar duct cells form a capsule around spermatozeugmata transforming them into spermatophores. The method of "sperm packaging" and morphology of spermatozeugmata are unique to the genus Zenarchopterus. They indicate that these fishes practice internal fertilization.